1. Gram-Negative Rods Related To the Enteric Tract THE ENTEROBACTERIACEAE
By:
Dr. Rania Ahmed
Assistant professor of Medical Microbiology and Immunology
Ain Shams University

2. It is a large family of Gram-negative rods.
Enterobacteriacae family includes many genera as:
Escherichia
Klebsiella, Enterobacter, Serratia
Proteus, Providencia, Morganella
Salmonella
Shigella
Yersinia.

3. Natural Habitat:
The majority are present as the normal flora in the colon of both man and animals (e.g. E. coli).
Some are saprophytes in water, soil and plants (e.g. Proteus) .
Few of them are primarily intestinal pathogens (e.g. Salmonella & Shigella )

4. General Characteristics of Enterobacteriaceae Family:
They are Gram-negative non spore forming, non-capsulate with few exceptions.
They are motile with peritrichate flagellae with few exceptions.
They can grow on ordinary media as well as on selective and differential media e.g. MacConkey’s agar

5. General Characteristics of Enterobacteriaceae Family:
According to growth on MacConkey’s agar
They are classified into:
Lactose fermenting e.g. E coli and Klebsiella
Non- lactose fermenting e.g. Proteus, Salmonella and Shigella
Late lactose fermenters

6. General Characteristics of Enterobacteriaceae Family:
They have 4 common characteristics:
Facultative anaerobe.
Ferment glucose
Oxidase negative but catalase positive.
Reduce nitrate to nitrite.
Differentiated by biochemical reactions & antigenic structure.

7. Antigenic structure: Three surface antigens (O, H & K):
O antigen (somatic antigen) is the outer polysaccharide portion of the lipopolysaccharide.
H antigen is the flagellar antigen.
K antigen is the capsular antigen.

8. ESCHERICHIA
This genus contains five species, the most important of which is Escherichia coli (E.coli).
Important Properties:
E. coli is a straight Gram negative bacilli, motile, may be capsulated.
E. coli ferments lactose, a property that distinguishes it from the two major intestinal pathogens, Shigella and Salmonella.

9. Normal habitat:
Gut of humans and animals; it is the most abundant facultative anaerobe in the colon and feces.
It may colonize lower end of urethra and vagina.

10. The antigenic structure:
Virulence Factors:
Pili.
Exotoxins (enterotoxins).
Capsule.
Motility.
Endotoxin.

11. Diseases caused by E.coli :
Urinary tract infection (UTI) :caused by uropathogenic E. coli
E.coli is the most common cause of UTI.
Neonatal meningitis: caused by E.coli strains having K1 capsular antigens
Different types of healthcare associated infections (HAIs) e.g. surgical site infections (SSI), catheter associated UTI (CAUTI), ventilator associated pneumonia (VAP), and intravascular device associated infections.
Diarrhea: caused by certain strains known as diarrheagenic E. coli.

12. Pathogenesis of E.coli infections:
Source of the E. coli
Diarrhea  is acquired by ingestion of food or water contaminated with human feces.
Urinary tract infections  the patient’s own colonic flora that colonizes the urogenital area.
Neonatal meningitis  the mother’s birth canal; the infection is acquired during birth.

13. Pathogenesis of Diarrhea:
Enterotoxigenic E. coli (ETEC):
Produces two enterotoxins: The heat- labile & heat stable toxin (LT):
The heat-labile toxin (LT)  stimulate adenylate cyclase  ↑intracellular cAMP  outpouring of fluid, K+ , Cl- from the enterocytes into the lumen of the gut  Watery diarrhea.
heat-stable toxin (ST)  stimulate guanylate cyclase ↑ intracellular cGMP  Watery diarrhea.

14. Pathogenesis of Diarrhea:
Enterohaemorrhagic E. coli (EHEC):
Produce Shiga- like toxins called verocytotoxins (VT) similar in action to Shiga toxin: Inhibit protein synthesis.  Bloody diarrhea.

15. Pathogenesis of Diarrhea:
Enterpathogenic E. coli (EPEC):
EPEC adhere to the mucosal cells of small intestine by pili, resulting in destruction of the microvilli  electrolyte imbalance and watery diarrhea.

16. Pathogenesis of Diarrhea:
Enteroinvasive E. coli (EIEC):
EIEC cause disease dysentery –like syndrome.
Virulence factors are nearly identical to Shigella species; that allow the invasion of mucosal epithelial cells of the large intestine and intracellular spread Tissue destruction
diarrhea, blood, mucous, and painful abdominal cramps

17. Pathogenesis of Diarrhea:
Enteroaggregative E. coli (EAEC): they are characterized by specific pattern of adherenc to intestinal cells in an aggregative manner by aggregative adherence fimbriae and production of heat stable (ST)-like toxin.
EAEC causes traveler's diarrhea and persistent diarrhea in children.

18. Pathogenesis of Neonatal meningitis & sepsis:
E.coli strains with K1 capsular antigen acquired by neonate through passage in birth canal invade the blood stream of infants from the nasopharynx or gastrointestinal tract causing sepsis and meningitis.

19. Pathogenesis of Urinary Tract Infections:
The bacteria colonize the periurethral area then ascend the urinary tract to cause UTI.
Pili  bind to specific receptors on the urinary tract epithelium.
Motility aids to ascend from:
Urethra into the bladder.
Ureter into the kidney.

20. KLEBSIELLA Important Properties:
Short Gram-negative rods, facultative anaerobes, non-motile, with very large polysaccharide capsule.
They can be found in water, soil, plants, insects, animals and humans.
Habitat: is the human large intestine and upper respiratory tract.
Antigenic Structure:
O antigen K antigen.

21. KLEBSIELLA
Species:
Two species produce diseases in man; can be differentiated by their capsular antigens.
Klebsiella pneumoniae:
The most common species responsible for majority of Klebsiella infections.
Includes 4 subspecies (they are sometimes called K. pneumoniae, K. aerogenes, K. ozanae, K. rhinoscleromatis).
Klebsiella oxytoca

22. Diseases caused by Klebsiella :
Community-acquired pneumonia: Necrosis, inflammation, and hemorrhage occur within lung tissue, sometimes producing thick, bloody, mucoid sputum described as currant jelly sputum (Fried-Lander pneumonia)
The illness typically affects middle-aged and older men with debilitating diseases such as alcoholism, diabetes, or chronic bronchopulmonary disease.
Health care associated infections (majority of Klebsiella infections) e.g. pneumonia, UTI, and SSI
Neonatal bacteremia & septicemia especially among premature infants and in neonatal intensive care units.

23. Transmission of Klebsiella causing infections:
Organism is transmitted to the lungs by aspiration from upper respiratory tract or by inhalation of respiratory droplets.
It is transmitted to urinary tract by ascending spread of fecal flora.
It is transmitted in hospitals by contact by contaminated hands of surrounded people in the hospitals or contact with contaminated equipment in hospitals e.g. catheters, respiratory devices.

24. Virulence factors of Klebsiella:
The huge polysaccharide capsule: It is the main virulence factor. It is antiphagocytic.
Lipopolysaccharides (LPS): fever and shock associated with sepsis.
Adhesins: These may be fimbrial or non-fimbrial. These help the microorganism to adhere to host cells.

25. PROTEUS SPECIES Important properties:
Short Gram-negative rods, highly motile.
High motility produces a striking swarming effect on some culture media as blood agar.
They produce the enzyme urease, which cleaves urea to form
ammonia & CO2.
These organisms are found in soil, water and human colon.

26. PROTEUS SPECIES Virulence factors:
The flagellum: vigorous motility of Proteus organisms may contribute to their ability to invade the urinary tract.
Pili: responsible for adhesion.
Endotoxins: responsible for induction of the inflammatory response.

27. PROTEUS SPECIES Mode of transmission:
Proteus spp. are part of the human intestinal flora and can cause infection upon leaving this location.
They may also be transmitted through contaminated catheters (particularly urinary catheters).
Diseases:
These organisms primarily cause urinary tract infections, both community- and hospital-acquired.
Other infections: septicemia and wound infections.

28. SALMONELLA Important characters:
Gram-negative, motile non-sporing rods, non capsulated except Salmonella typhi (S. typhi) and S.paratyphi C which possess Vi antigen.

29. SALMONELLA Natural Habitat:
All salmonellae are obligate parasites.
S. typhi: Man is the only reservoir.
Other species of salmonellae have a significant animal as well as human reservoir:
The most frequent animal source is poultry and eggs of animals.

30. SALMONELLA Antigenic structure:
It displays 3 antigens cell wall O, flagellar H, and capsular Vi.
Salmonellae are divided into serogroups according to O (somatic) antigens and then into serotypes according to specific H (flagellar) antigens.
Some possess Vi (capsular) antigens.

31. SALMONELLA Virulence factors: Fimbriae: attachment to host cells.
Intracellular pathogen: can survive & multiply within macrophages.
Capsule (Vi): of S. typhi and S.paratyphi C, which is antiphagocytic.

32. SALMONELLA Virulence factors:
Phase variation of H antigens, which varies from group specific (phase II) to species specific (phase I).
This variation helps the organism to evade the immune system.

33. Infections caused by Salmonella:
Enteric fever caused by Salmonella typhi (typhoid fever) & S. paratyphi A, B and C (paratyphoid fever).
Salmonella food poisoning (Salmonella enterocolitis) is caused by S. typhimurium and S. enteritidis.
Bacteremia with focal lesions in lungs, meninges, and bones is caused by S. choleraesuis.

34. Pathogenesis Of Enteric Fever:
Mode of transmission
Ingestion of contaminated food or water by the excreta of a case or a carrier (fecal or urinary carrier).
Occasionally through direct contact with patients or carriers.

35. Pathogenesis Of Enteric Fever:
Onset of disease

36. Pathogenesis Of Enteric Fever:
Carrier

37. Salmonella Food Poisoning "Salmonella Enterocolitis"
Transmission:
Inadequately cooked poultry and eggs (common source) or meat products.
Contaminated food by excreta of animals e.g. rats.
Human sources: patient during enterocolitis attack or chronic carriers.

38. Salmonella Food Poisoning "Salmonella Enterocolitis"
Pathogenesis:
Invasion of the small and large intestines.
Resulting in inflammation and diarrhea.
Neutrophils limit the infection to the gut and the adjacent mesenteric lymph nodes; bacteremia is infrequent in enterocolitis.

39. Salmonella Bacteremia with Focal Lesions
Transient or persistent bacteremia.
Mode of transmission of focal lesions: by Blood
Bacteremia with localized foci resulting in persistent infection of many organs with osteomyelitis, pneumonia, and meningitis as the most common sequelae.

40. SHIGELLA Important properties:
Gram-negative rods, Non-motile, Non-capsulate& Facultative anaerobe.
Shigella is a true human pathogen, for which there is no animal reservoir.

41. SHIGELLA Classification:
The genus Shigella has 4 species or subgroups (A, B, C, and D) & several serotypes.
Subgroups and serotypes are differentiated from each other by their biochemical characteristics and antigenic properties.
1. Group A = Shigella (Sh.) dysenteriae
2. Group B (Sh. flexneri)
3. Group C (Sh. boydii)
4. Group D (Sh. sonnei)

42. SHIGELLA
Virulence:
Attachment & penetration of mucosal epithelial cells of large intestine.
Intracellular spread proteins: facilitate transfer of bacteria to adjacent cells.
Shiga Toxin:

43. Pathogenesis: Infection is limited tointestinal tract.
Epithelial cell M cell
Macrophages shigella
Shigella pass through M cells to
reach the submucosa. Macrophages
take up the bacilli, die and release the
bacteria.
The bacteria enter epithelial cells
from their basolateral aspect by
endocytosis.

44. The endocytotic vacuoles lyse releasing the bacteria into the cytoplasm. The bacteria move intracellularly and spread to adjacent cells. Infected cells die leading to an acute inflammatory response with migration of neutrophils to the epithelial side

45. SHIGELLA Virulence: Shiga Toxin:
It is produced by Shigella dysenteriae type 1.
It has the following characters:
Enterotoxic, neurotoxic and cytotoxic activity.
Encoded by chromosomal genes.
Similar to the Shiga-like toxin of enterohemorrhagic E. coli (EHEC) 0157:H7 strain except that Shiga-like toxin is encoded by lysogenic bacteriophage.

46. SHIGELLA Virulence: Shiga toxin cytotoxic activity:
Damage to epithelial cells of intestine:
Inhibit protein synthesis, causing cell death
vascular damage to the intestine, and hemorrhage (blood and fecal leukocytes in stool).
Damage to glomerular endothelial cells, leading to haemolytic uremic syndrome (HUS).

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